Printing method and apparatus having multiple raster image processors

ABSTRACT

A multiple raster image processor (“RIP”) system is described that enables faster system performance over multiple processors, and includes a zero RIP feature consisting of a language interpreter sub-RIP that interprets a print instruction file but does not process the graphics rendering steps or the post-language processing operators. A skip RIP interprets selected pages in a way that skips all or most of the processing for that page. Pages to be skipped are scheduled for a different processor, thereby saving processing time and enabling the provision of a multiple processor RIP.

REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.09/770,856, filed Jan. 26, 2001, now U.S. Pat. No. 6,559,958, which is acontinuation of U.S. application Ser. No. 09/298,639, filed Apr. 23,1999, now U.S. Pat. No. 6,327,050, which is a non-provisionalapplication of U.S. provisional application Ser. No. 60/098,125, filedAug. 27, 1998.

FIELD OF THE INVENTION

This invention relates to printing images that exist in a digitalelectronic format. More particularly, the invention relates to aprinting methods and apparatus having multiple raster image processors.

BACKGROUND

Every image that exists in a digital electronic format is made ofpicture elements. At some point, all such digital image data, whetherexpressed as vector format data or bitmap format data, must be renderedinto pixels for display on a monitor or for printing on a printer. Allimages, therefore, have pixels as their base. Rendering, or translatingthe digital data into physical output, is the most important part ofrealizing such images. Raster image processing (“RIP”) refers to theprocess of translating digital image data into physical visual imagesand graphics.

Referring now to FIG. 1, a previously known RIP is described. In rasterimage processing, each horizontal line of bitmap image pixel informationis referred to as a scan line or raster line. In FIG. 1, Postscript®lines and/or digital RGB or CMYK pixels 12 are shown processed byassociated RIPs 13-15 to produce information that results in a physicaloutput 16. Simple output devices translate only one raster line at atime and then output that line to film, paper, or a monitor. FIG. 2 isan illustration of an image 20 and a single raster line 22 as processedby such a device. More efficient RIP techniques analyze an entire imageand convert the image information to visual output.

A RIP is a program that may be embedded in hardware or software. Ahardware RIP is a computer that is attached to an output device andwhich is dedicated to translating digital image data for output. Imagedata are sent from a workstation to a computer that is attached to theoutput device. The hardware RIP program which resides in this computerinterprets the image data and provides raw ON/OFF instructions to theoutput device. The actual interpreter may be any program that translatesimage information in accordance with a known format. For example, thePostscript® interpreter manufactured by Adobe Corporation of MountainView, Calif., is commonly used in raster image processing.

A software RIP performs many of the same functions as a hardware RIP.The software RIP is usually located at a workstation that is notnecessarily dedicated solely to the RIP function. The software RIPinterprets the digital image data and produces therefrom informationthat is required for the output device to properly function. A majordisadvantage of software RIPs is that the workstation may not beconfigured to perform at speeds equal to a dedicated hardware RIP.Software RIPs are also presently less desirable for larger printfacilities because such RIPs usually require a large amount of free harddisk space on the workstation. Such hard disk storage is necessarybecause all of the digital data that are processed must be saved beforethey are sent to the output device.

The RIPing process is complex and much of the output device rating isbased upon the device's image processing speed. The speed of theinterpreter or RIP is a major factor in the efficiency of the entireimage reproduction process. Because of the dedicated computer, hardwareRIPs are typically faster than software RIPs. Even so, it would beadvantageous to provide improvements in RIP architectures that increaseprocessing speed and efficiency.

SUMMARY

The invention provides multiple RIP systems, which comprise a scalablearchitecture that enables faster system performance over multipleprocessors. Systems in accordance with this invention include thefollowing features:

Zero RIP: A language interpreter sub-RIP that interprets a printinstruction file but does not process the graphics rendering steps orthe post-language processing operators. The zero RIP provides severalbenefits over conventional RIP technology. For example, the zero RIPdiscovers page related attributes for individual pages within amulti-page job and reports any potential errors or warnings with thefile.

Thumb RIP: A very low resolution RIP that is used specifically forcreating thumbnail images. The thumb RIP is much faster than a fullresolution RIP process and requires less system resources than a fullresolution RIP. The thumb RIP creates a small thumbnail image forviewing or for other purposes (e.g., toner estimation).

Push data flow: Some benefits of this feature of the invention include areduction in concurrent bus contention on a shared bus leading to theprocessors. This aspect of the invention also reduces overhead on a busleading to the processors and saves time by reducing the number ofprocessing steps.

Skip RIP: This feature of the invention interprets selected pages in amanner that skips all or most of the processing for that page. Pages tobe skipped are scheduled for a different processor. This approach savesprocessing time and enables the provision of a multiple processor RIP.Skipping techniques include all or some of the following: RIP to low orzero resolution, skip the rendering step for the pages, skip thecompression step for the pages, and change selected Postscript® commandsfor the pages.

Rules based scheduler on a page/face basis: This feature of theinvention supports a dynamic assignment and assessment algorithm.Scheduling results in optimum use of available resources and requestedprint constraints (e.g., constrained time window) and optimum use ofsystem bandwidth (e.g., bandwidth control).

Archiving and editing capability: This feature of the invention is anintegrated system that enables tagged archiving of jobs or parts of jobsin a post-RIPed (i.e., raster) format, for example, in a special cachelocated within the multi-RIP system.

Parallel RIPing using multiple processors: This feature of the inventionuses multiple processors in the system, either on a single document oron more than one document.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned objects and features of the present invention can bemore clearly understood from the following detailed descriptionconsidered in conjunction with the following drawings, in which the samereference numerals denote the same elements throughout, and in which:

FIG. 1 is a block diagram of a conventional raster image processingsystem;

FIG. 2 is a drawing that illustrates the processing of a single rasterimage line;

FIG. 3 is a block diagram of an exemplary multiple RIP system inaccordance with this invention;

FIG. 4 is a flow diagram showing RIPing in a conventional raster imageprocessing system;

FIG. 5 is a flow diagram showing exemplary RIPing in a multiple RIPsystem in accordance with this invention; and

FIG. 6 is a block diagram of another exemplary multiple RIP system inaccordance with this invention.

DETAILED DESCRIPTION

The multiple RIP system disclosed herein is a scalable architecturewhich enables faster system performance over multiple processors. Thesystem includes the following features:

Zero RIP: A language interpreter sub-RIP that interprets the printinstruction file but does not process the graphics rendering steps orthe post-language processing operators. The zero RIP uses modificationsto the setting of the standard PostScript interpreter and processes thePostScript stream in its entirety, but does not execute graphic commandsbeyond some minimum that is necessary to preserver the integrity of thePostScript processing. The zero RIP provides several benefits overconventional RIP technology. For example, the zero RIP discovers pagerelated attributes for individual pages within a multi-page job andreports any potential errors or warnings with the file.

Thumb RIP: A very low resolution RIP that is used specifically forcreating low resolution thumbnail images. Two methods are implementedfor the generation of thumbnails in exemplary embodiments of theinvention. The first method uses sub-sampling techniques applied to thefull resolution rendered page. In the second method, the rendered pagecan be generated in multiple formats, e.g., any bit depth per colorplane and multiple compression techniques. The thumb RIP is much fasterthan a full resolution RIP process and requires fewer system resourcesthan a full resolution RIP. The thumb RIP creates a small thumbnailimage for viewing or for other purposes (e.g., toner estimation). Itshould be appreciated that a thumbnail could also be generated elsewherein the system.

Push data flow: For purposes of the discussion herein, a push data flowmodel refers to an entire print job that is pushed to a RIP by a printserver, while a pull data flow model refers to pages of a print job thatare pulled from the print server by the RIP. Some benefits of thisfeature of the invention include a reduction in concurrent buscontention on a shared bus leading into the processors. This aspect ofthe invention also reduces overhead on a bus leading to the processorsand saves time by reducing the number of processing steps.

Skip RIP: This feature of the invention interprets selected pages in away to skip all or most of the processing for that page. In an exemplaryembodiment of the invention, the skip RIP is implemented using a jobticket technology. The job tickets enumerate for a specific RIP (i.e.,the interpreter) which pages to render. The job ticket is processedaccording to the actual document's page description language. In thecase of documents in the PDF format, the ability to skip pages is partof the language definition. In the case of other page descriptionlanguages, e.g., PostScript and PCL, the standard interpreter setting ismodified to allow page skipping, for example using the zero RIPdiscussed above. Pages to be skipped are scheduled for a differentprocessor. This approach saves processing time and enables the provisionof a multiple processor RIP.

Skipping techniques include all or some of the following:

-   -   RIP to low or zero resolution.    -   Skip the rendering step for these pages.    -   Skip the compression step for these pages.    -   Change selected Postscript® commands for these pages.

Rules based scheduler on a page/face basis: This feature of theinvention supports a dynamic assignment and assessment algorithm.Scheduling also may be based on printer characteristics, e.g., colorpages sent to a color printer and black and white pages sent to amonochrome printer. Scheduling is based on the job characteristicsavailable from a current job ticket associated with the job. Job ticketinformation includes, for example, analysis of the page complexity,color spaces, and print engine requirements. The scheduler maintains thedynamic state of the available RIPs. For example, the characteristics,such as supported page sizes, finishing options, color or black andwhite, and the current load on each RIP. The scheduler uses the pageinformation and the RIP information to assign a page to a RIP. Theassigned page includes RIPing instructions and the target printingdevice as part of the job ticket. Scheduling results in optimum use ofavailable resources and requested print constraints (e.g., constrainedtime window) and optimum use of system bandwidth (e.g., bandwidthcontrol).

Archiving and editing capability: This feature of the invention is anintegrated system that enables tagged archiving of jobs or parts of jobsin a post-RIPed (i.e., raster) format in a special cache located withinthe multi-RIP system. For purpose of this invention, tagging refers tothe ability of the user or operator to tag or otherwise designate whichjobs or parts of jobs should be automatically archived and in whichformat.

Parallel RIPing using multiple processors: This feature of the inventionuses multiple processors, either on a single document or on more thanone document.

System Data Flow

FIG. 3 is a block diagram of an exemplary multiple RIP system inaccordance with this invention. A system controller (not shown) receivesall jobs to be printed. The print instruction file 30 can be aPostScript, PCL, or other page description language data stream. Filesare queued in the file spooler 31 for the pre-RIP (or Zero RIP) 32. Thepre-RIP 32 performs a zero resolution RIP on the file, and generates amap 33 of page attributes, which attributes may include, for example,page size, complexity, and number of print separations (e.g., black andwhite, color, varnish, and high fidelity color). Next, a scheduler 34assigns pages to specific processors 35-37, based on availability statusprovided by the processors, and also based on the map of page attributesfrom the pre-RIP. Then, the scheduler sends the original printinstruction file to all of the processors, as well as a list 38 of whichpages are assigned to which processor. As the processors complete theRIP step on their assigned pages, they make available the completedpages to the combiner 39, where the pages are combined into the final,ordered raster job.

System Components

Zero Rip

The zero RIP (or pre-RIP) is an extremely fast sub-RIP that can processa full PDL file in less than one percent of the time it would take for aconventional RIP. The pre-RIP) works this fast because it only engagesthe steps needed to get the resulting information that is needed.Operation of the zero RIP is discussed above. FIG. 4 provides an exampleof two back-to-back pages being RIPed in a conventional RIP.Post-language processing includes such steps as enhancements, thumbnailgeneration, compression and storage. FIG. 5, in contrast, illustratesthe same two pages processed through the zero RIP. As discussed above,the zero RIP is a sub-RIP that interprets the print instruction file butdoes not process the graphics rendering steps or the post-languageprocessing operators. The output of the zero RIP is the following set ofattributes per page:

-   -   Number of colors—e.g., monochrome, two color, four color, six        color.    -   Finishing options.    -   Estimated time that page takes to RIP. An exemplary embodiment        of the invention predicts this time by counting painting        operators and by using other attributes in this list to        calculate a value.    -   Page size.    -   Simplex/Duplex.    -   Any errors or missing resources.        Adaptive Scheduler

The multiple RIP system automatically splits incoming jobs using thescheduler to optimize the system based on changing needs, minute byminute. For example, if there is a rush job to print, a user may selecta rush request option on a job ticket and that job is automaticallyrushed through the system and split across the optimum number of RIPsfor fastest available printing time. The system administrator canconfigure the system to allow only selected users the rush option. Forpurposes of the invention, it will be appreciated by those skilled inthe art that the scheduler is comprised of any well known print driverthat provides scheduling functions. Such print driver is modified in amanner readily apparent to those skilled in the art in view of thedisclosure herein to add user options with regard to the multiple RIPfeatures described herein.

Another example of the invention involves a large job that is in theprint queue along with several small jobs. The scheduler technologysaves at least one of the plural RIPs for small jobs to keep the printengines operating and gives the rest of the needed RIPs to the largejob. If multiple print engines are connected to the system, thescheduler routes the pages or jobs to the designated engine or the mostcost effective engine for that particular job, based on user job ticketselections. The system can receive jobs over network or media to onesmart queue and automatically assign the job to the optimal RIP(s) andprint engine(s), while sending the client up to the minute status.

The scheduler takes the following dynamic inputs:

-   -   Requested priority or fixed time window.    -   Cost—different engines have different costs.    -   Number of colors, e.g. monochrome, two color, four color, or six        color.    -   Finishing options    -   Estimated time that the RIPs are busy, i.e., amount of work left        per processor.    -   Optimal print engine loading, e.g., to keep a single engine        cycled up for a highest percentage time and for multiple        engines.    -   Long jobs—schedule to one engine, one RIP. For purposes of the        discussion herein, a long job is a job that begins printing        before it is fully spooled into the file spooler (e.g. the        printing of a batch of telephone bills).    -   Batching of related page types to a RIP to optimize resources        and to maximize performance.

The following are static inputs (i.e., inputs that change infrequently):

-   -   Administrative configuration:        -   Example 1: Frees one RIP if pending small jobs (<100 pages            or 40 MB) for optimal printer loading, especially if            multiple engines are provided.        -   Example 2: Optimizes for incoming job load by using an            adaptive algorithm. For example, if the system normally            reserves one RIP for smaller jobs and dedicates the other            RIPs to larger jobs, it may be determined that the one RIP            remains idle at such time as there are many larger jobs and            no smaller jobs. The system adapts to this dynamic and            releases the reserved RIP for use with larger jobs.

The output of the scheduler provides adaptive control, i.e., the abilityto monitor actual system demands and operation and alter predeterminedpreferences in accordance therewith, over the following:

-   -   Which pages/faces are sent to which processor (RIP) and when and        what order are they RIPed.    -   Which pages/faces are sent to which print engine and in what        order.    -   Addition of a cover or slip sheet where applicable for a post        processing step        Combiner

The combiner receives and re-orders the incoming pages and faces. Thefollowing pseudo code shows the an exemplary combiner function inaccordance with this invention:

RIP:

-   -   Page processing Done.    -   Send message with jobnumber, pagenumber, it's IP address to VPM    -   When asked by VPM, transfer the real page buffer.    -   When asked by VPM, free the page buffer memory.    -   Continue this with every page that it processes.

VPM:

-   -   (It maintains a list of job/page numbers already processed by        all the RIPs)        -   Get message from RIP about the page        -   Is this the next expected job/page number.        -   If (Yes) /* Yes */            -   Send message to RIP asking it to send the real page                buffer.            -   Send message to RIP asking it to free the page buffer                memory.            -   Is the next page, required, in the list?            -   If (Yes)                -   repeat the process.        -   Else /* No, not the expected page number */            -   Save the message in the list.                Processor

Each processor (or set of processors sharing one system memory) has aRIP application running on it. Each RIP can process any one of multiplepage description languages (PDLs), for example PDF, PS, and PCL. Forpurposes of implementing the invention described herein, those skilledin the art will appreciate that any standard hardware or software RIPmay be used in connection with the various modules which comprise theinvention. Further, the invention is intended for use in an environmentthat supports a hot pluggable interconnect. As such, additional RIPs maybe added to the system while the system is in operation. The systemrecognizes such additional RIPs as they are added and assigns jobs tothem (or receives requests for pages from them) without interruption innormal system operation.

Control

An exemplary embodiment of the invention tags the information on eachpage using a job ticketing technique. For purposes of the inventionherein, tagging refers to the known technique of placing all jobattributes into a ticket or tag which, in exemplary embodiments of theinvention, is generated by the multi-RIP system. Such tags preferablyinclude client preferences and job attributes.

FIG. 6 is a block schematic diagram of a multiple RIP system accordingto an exemplary embodiment of the invention. In this embodiment, a jobserver 62 is connected to a network 60. Job server 62 receives printjobs from various entities connected to the network, and includes amonitor 61 and a keyboard 63, although it is not necessary that thesecomponents be provided. For example, job server 62 could be an embeddedserver. Job server 62 is implemented on a PC platform and includes a PCIcard slot 69 that receives an integrated compression PCI card 68. Thiselement of the system is not required by the invention. The actualoperation and constituent elements of the job server are shown in FIG.3.

Job server 62 provides pages to each of multiple RIPs 66 and 67. Themultiple RIP processor system provides significant improvement inperformance over that of a single RIP system. Although two RIPs areshown in FIG. 6, the system can support any number of RIPs as may bedesired. Each RIP in this embodiment of the invention includes a PCIcard slot 71 and 73 that receives an integrated compression PCI card 70and 72. This element of the system is not required by the invention.

The RIPs are connected to one or more video print machines 64 via a highspeed interconnect bus 74. The video print machine provides output to aprint engine 75 and includes a redundant array of inexpensive disks(“RAID”) 65, which is an acceleration system that is known in the art.Although FIG. 6 shows multiple RIPs connected to a single print engine,it should be appreciated the each RIP may be connected to a different,dedicated print engine, or the RIPs may be dynamically assigned to anyof a plurality of print engines as determined by the scheduler.

The foregoing merely illustrates the principles of this invention, andvarious modifications can be made by persons of ordinary skill in theart without departing from the scope and spirit of this invention.

1. A raster image processing system, comprising: a plurality of rasterimage processors; and a rules based scheduler for assigning pages of aninput print instruction file to the plurality of raster imageprocessors, wherein the rules based scheduler is adapted to respond to arush request option in a print job ticket by rushing the print jobthrough the system and splitting the print job across the plurality ofraster image processors for the fastest available printing time.
 2. Theraster image processing system of claim 1, further comprising: a lowresolution RIP that creates a thumbnail image of a portion of the inputprint instruction file.
 3. The raster image processing system of claim1, wherein the system performs parallel raster image processing usingsaid multiple raster image processors.
 4. A raster image processingsystem comprising a job server connected to a network for receivingprint jobs from various entities connected to said network, the jobserver adapted to provide a page of each of the print jobs to acorresponding one of a plurality of raster image processors, and toreceive requests for pages from the raster image processors, wherein thejob server comprises: a system controller for receiving printinstruction files comprising information to be printed by the rasterimage processors; and a scheduler for assigning pages to specific onesof the raster image processors based on availability status provided bythe raster image processors, and wherein the scheduler is adapted torespond to a rush request option in a print job ticket by rushing theprint job through the system and splitting the print job across theplurality of raster image processors for the fastest available printingtime.
 5. The system of claim 4, wherein each raster image processor isconnected to a single, dedicated print engine.
 6. The system of claim 4,wherein each raster image processor is connected to a different,dedicated print engine.
 7. The system of claim 4, wherein each rasterimage processor is dynamically assigned to any of a plurality of printengines.